Spa shell



FIG. 1 is a top front perspective view of a spa shell, showing my new design;

FIG. 2 is a top plan view thereof; and,

FIG. 3 is a side view thereof, with all other sides being identical.

The bottom of the article is plain and unornamented.

The broken line showing in FIGS. 1 and 3 is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a spa shell, as shown and described. 